1. Field of the Invention
This invention is in the field of intracellular detection of enzymes using fluorogenic or fluorescent probes. The invention relates to novel fluorescent dyes and application of these dyes for the preparation of novel fluorogenic or fluorescent peptide or amino acid derivatives which are substrates of proteases and peptidases. In particular, the invention relates to novel fluorogenic or fluorescent peptide derivatives which are substrates of enzymes involved in apoptosis, such as caspases and the lymphocyte-derived serine protease Granzyme B. The invention also relates to a process for measuring the activity of caspases and other enzymes involved in apoptosis in living or dead whole cells, cell lines or tissue samples derived from any healthy, diseased, infected or cancerous organ or tissue. The invention also relates to the use of the fluorogenic or fluorescent substrates in a novel assay system for discovering or detecting inhibitors or inducers of apoptosis in compound collections or compound libraries. Furthermore, the invention relates to the use of the fluorogenic or fluorescent substrates in determining the sensitivity of cancer cells to treatment with chemotherapeutic drugs. The invention also relates to novel fluorogenic or fluorescent peptide derivatives which are substrates of exopeptidases such as arninopeptidase A and N, methionine aminopeptidase and dipeptidyl-peptidase IV, endopetidases such as calpain, proteases such as HIV proteases, HCMV protease, HSV protease, HCV protease and adenovirus protease.
2. Related Art
Organisms eliminate unwanted cells by a process variously known as regulated cell death, programmed cell death or apoptosis. Such cell death occurs as a normal aspect of animal development as well as in tissue homeostasis and aging (Glucksmann, A., Biol. Rev. Cambridge Philos. Soc. 26:59-86 (1951); Glucksmann, A., Archives de Biologie 76:419-437 (1965); Ellis et al., Dev. 112:591-603 (1991); Vaux et al., Cell 76:777-779 (1994)). Apoptosis regulates cell number, facilitates morphogenesis, removes harmful or otherwise abnormal cells and eliminates cells that have already performed their function. Additionally, apoptosis occurs in response to various physiological stresses, such as hypoxia or ischemia (PCT published application W096/20721).
There are a number of morphological changes shared by cells experiencing regulated cell death, including plasma and nuclear membrane blebbing, cell shrinkage (condensation of nucleoplasm and cytoplasm), organelle relocalization and compaction, chromatin condensation and production of apoptotic bodies (membrane enclosed particles containing intracellular material) (Orrenius, S., J. Internal Medicine 237:529-536 (1995)).
Apoptosis is achieved through an endogenous mechanism of cellular suicide (Wyllie, A. H., in Cell Death in Biology and Pathology, Bowen and Lockshin, eds., Chapman and Hall (1981), pp. 9-34). A cell activates its internally encoded suicide program as a result of either internal or external signals. The suicide program is executed through the activation of a carefully regulated genetic program (Wylie et al., Int. Rev. Cyt. 68:251 (1980); Ellis et al., Ann. Rev. Cell Bio. 7:663 (1991)). Apoptotic cells and bodies are usually recognized and cleared by neighboring cells or macrophages before lysis. Because of this clearance mechanism, inflammation is not induced despite the clearance of great numbers of cells (Orrenius, S., J. Internal Medicine 237:529-536 (1995)).
Mammalian interleukin-1xcex2 (IL-1xcex2) plays an important role in various pathologic processes, including chronic and acute inflammation and autoimmune diseases (Oppenheim, J. H. et. al. Immunology Today, 7, 45-56 (1986)). IL-1xcex2 is synthesized as a cell associated precursor polypeptide (pro-IL-1xcex2) that is unable to bind IL-1 receptors and is biologically inactive (Mosley et al., J. Biol. Chem. 262:2941-2944 (1987)). By inhibiting conversion of precursor IL-1xcex2 to mature IL-1xcex2, the activity of interleukin-1 can be inhibited. IL-1 is also a cytokine involved in mediating a wide range of biological responses including inflammation, septic shock, wound healing, hematopoiesis and growth of certain leukemias (Dinarello, C. A., Blood 77:1627-1652 (1991); diGiovine et al., Immunology Today 11:13 (1990)). Interleukin-1xcex2 converting enzyme (ICE) is a protease responsible for the activation of interleukin-1xcex2 (IL-1xcex2) (Thornberry, N. A., et al., Nature 356:768 (1992); Yuan, J., et al., Cell 75:641 (1993)). ICE is a substrate-specific cysteine protease that cleaves the inactive prointerleukin-1 to produce the mature IL-1. The genes that encode for ICE and CPP32 are members of the mammalian ICE/Ced-3 family of genes which presently includes at least twelve members: ICE, CPP32/Yama/Apopain, mICE2, ICE4, ICH1, TX/ICH-2, MCH2, MCH3, MCH4, FLICE/MACH/MCH5, ICE-LAP6 and ICEre1III. The proteolytic activity of this family of cysteine proteases, whose active site cysteine residue is essential for ICE-mediated apoptosis, appears critical in mediating cell death (Miura et al., Cell 75:653-660 (1993)). This gene family has recently been named caspases (Alnernri, E. S. et. al. Cell, 87:171 (1996)). A death trigger, such as Tumor Necrosis Factor, FAS-ligand, oxygen or nutrient deprivation, viruses, toxins, anti-cancer drugs etc., can activate caspases within cells in a cascade-like fashion where caspases upstream in the cascade (e.g. FLICE/MACH/MCH5) can activate capsases further downstream in the cascade (e.g. CPP-32/Yama/Apopain). Activation of the caspase cascade leads to cell death.
A wealth of scientific evidence suggests that, in many diseases, the caspase cascade is activated when it shouldn""t be. This leads to excessive cellular suicide and organ failure. Diseases involving inappropriate activation of the caspase cascade and subsequent cellular suicide include myocardial infarction, congestive heart failure, autoimmune diseases, AIDS, viral infections, kidney failure, liver failure, rheumatoid arthritis, ischemic stroke, neurodegenerative diseases, atherosclerosis etc. Therefore, the discovery of novel drugs that can block or inhibit the activation of the caspase cascade would have wide-ranging impact on the treatment of degenerative diseases of most, if not all, organ systems of the human body.
Caspases are also thought to be crucial in the development and treatment of cancer. There is mounting evidence that cancer cells, while containing caspases, lack parts of the molecular machinery that activate the caspase cascade (Los et al., Blood, Vol. 90, No 8:3118-3129 (1997)). This causes the cancer cells to lose their capacity to undergo cellular suicide and the cells become immortalxe2x80x94they become cancerous.
It has been shown that chemotherapeutic (anti-cancer) drugs can trigger cancer cells to undergo suicide by re-activating the dormant caspase cascade. This may be a crucial aspect of the mode of action of most, if not all, known anticancer drugs (Los et al., Blood, Vol. 90, No 8:3118-3129 (1997); Friesen et al., Nat. Med 2:574 (1996). Chemotherapeutic drugs may differ in their capacity to activate the caspase system in different classes of cancers. Moreover, it is likely that anti-cancer drugs differ in their ability to activate the caspase cascade in a given cancer (e.g. lung cancer) and in different patients. In other words, there are differences from one patient to another in the chemosensitivity of, e.g. lung cancer cells, to various anti-cancer drugs.
In summary, the excessive activation of the caspase cascade plays a crucial role in a wide variety of degenerative organ diseases, while a non-functioning caspase system is a hallmark of cancer cells. New drugs that inhibit or stimulate the caspase cascade are likely to revolutionize the treatment of numerous human diseases ranging from infectious, cardiovascular, endocrine, kidney, liver and brain diseases to diseases of the immune system and to cancer.
In order to find drugs that either inhibit or stimulate the caspase cascade, it is necessary to develop high-throughput caspase activation (HTCA) assays. These HTCA assays must be able to monitor activation or inhibition of the caspase cascade inside living or whole cells. Ideally, HTCA assays should be versatile enough to measure the caspase cascade activity inside any living or whole cell, no matter what its origin might be: Cancer cells, tumor cells, immune cells, brain cells, cells of the endocrine system, cells or cell lines from different organ systems, biopsy samples etc. Furthermore, such HTCA assays should be able to measurexe2x80x94within living or whole cellsxe2x80x94the activation or inhibition of any of the caspase enzymes or any other enzymes that are involved in the caspase cascade. Developing such versatile HTCA assays represents a substantial advance in the field of drug screening.
Currently available HTCA assays do not permit inner cellular screening for compounds that can either activate or inhibit the caspase cascade. There are only cell-free, high-throughput screening assays available that can measure the activity of individually isolated caspase enzymes, or assays that can measure the activity of caspases in dead cells which have been permeabilized by osmotic shock, for example (Los et al., Blood, Vol. 90, No 8:3118-3129 (1997)). But these enzyme assays cannot predict the effect of a compound on the caspase cascade in living cells for the following reasons:
1.) Cell free assays, or assays using dead, permeabilized cells, cannot predict the ability of compounds to penetrate the cellular membrane. This is crucial because the caspase cascade resides in the interior of the cells. In order to be active, a compound must not only be able to modulate the caspase enzyme or enzymes, but it must also be able to penetrate the intact cell membrane. Cell-free assays or assays using dead cells are therefore unable to determine whether or not a compound will be potentially useful as a drug.
2.) Isolated caspases in cell-free assays are highly susceptible to oxidation and to compounds that can cause oxidation of the enzymes. This property of isolated caspases makes cell free caspase screening assays highly susceptible to artifacts and has precluded successful use of these assays for high-throughput screening of combinatorial (or other) chemical libraries. Previous mass screening efforts, using cell-free caspase enzyme assays, have led to discovery of numerous inhibitors which oxidize caspases, but no compound that would be useful as a potential drug. Similar difficulties have been reported by others.
3.) Numerous cellular receptors, proteins, cell constituents and cofactorsxe2x80x94many of which are still unknownxe2x80x94can influence the caspase cascade in living cells. Cell-free caspase assays or assays using permeabilized, dead cells do not take into account these cellular receptors and cofactors. Because of this, it is possible that a compound identified in a cell-free or dead-cell caspase assay will not work in living cells. On the other hand, a compound that might inhibit or stimulate the caspase cascade indirectly through one of the cellular receptors or cofactors would be missed entirely in an cell-free or dead-cell caspase assay.
4.) It is highly likely that the caspase cascade functions differently in cells derived from different organs. There is growing evidence that the receptors and cofactors that influence the caspase cascade differ among cell types. Using cell-free or dead cell assays, it would be virtually impossible to identify cell-type or organ specific modulators of the caspase cascade.
A potentially important application of a HTCA assay system for measuring intracellular caspase enzymes or any other enzymes involved in apoptosis is chemosensitivity testing of human cancers. It is known that there is a genetic difference in the susceptibility of human cancers to the currently marketed anti-cancer drugs: For example, lung cancer cells in one patient might be sensitive to Drug A, while another patient""s lung cancer might be insensitive to Drug A, but sensitive to Drug B. This pharmacogenetic difference in chemosensitivity of cancer cells from different individuals is a well-known phenomenon.
In the past, attempts have been made to determine the chemosensitivity of cancer cells taken from individual patients prior to designing a treatment regimen with one or more of the marketed anti-cancer drugs. However, chemosensitivity testing has not found wide-spread use, because the procedures involved have some inherent technical difficulties: The testing is very time consuming (six or more days per screen) and it requires culturing of the cells prior to screening. The cell culture leads to clonal selection of cells and the cultured cells are then no longer representative of the cancer in the patient. A HTCA assay system for quickly measuring intracellular caspase activity could be used to determine very rapidly the chemosensitivity profile of freshly excised cancer cells. If the assay has a high throughput, it would be feasible to test chemosensitivity of multiple samples taken from the same patient, e.g. from different metastases. This information could then be used to design a treatment regimen using combinations of marketed anti-cancer drugs to which the cells showed greatest sensitivity.
It is clear that the need exists for HTCA assays and reagents for such assays that can be employed in drug discovery or diagnostic procedures to quickly detect and measure the activity of compounds that activate or inhibit the caspase cascade or other enzymes involved in apoptosis in the interior of living or dead whole cells. A reagent for this type of cell assay ideally should meet the following conditions: a) there should be a big difference in fluorescence signal between peptide-reporter molecule and reporter molecule after the amide bond in peptide-reporter is cleaved by the caspases or other enzymes involved in apoptosis, preferably the peptide-reporter molecule should be non-fluorescent and most preferably the peptide-reporter molecule should be non-fluorescent and colorless; b) the peptide-reporter molecule should be cell permeable, therefore there should be minimum numbers of hydrophilic groups in the molecule and the size of the molecule should preferably be small; c) the peptide-reporter molecule should preferably not diffuse out of the cell once it permeates the cell membrane; d) the reporter molecule should preferably not diffuse out of the cell once it is liberated from the peptide.
The method of screening apoptosis inhibitors or inducers in whole cells vs cell-free enzyme assay can also be used for the screening of inhibitors of enzymes other than caspases. Traditionally, enzyme inhibitors were first identified by cell-free enzyme assays. Cell cultures were then used for secondary assay to assess activity of the active compounds in intact cells. A cell permeable fluorogenic or fluorescent substrate will enable the screening of inhibitors of proteases and peptidases and other enzymes directly in living whole cells. There are several advantages in whole cell assays vs cell-free enzyme assays. One of the advantages is that in whole cell assays, the inhibitor will have to penetrate the cell to be detected. Since many proteases in living cells are regulated by other proteins, receptors or genes, screening using living cells will allow the identification of small molecule compounds which interfere with cellular proteases by binding to the active site, as well as compounds which modulate protease function by interfering with transcription, translation, biosynthesis, sub-unit assembly, cellular cofactors or signal transduction mechanisms (or viral entry into host cells, in the case of viral proteases). Furthermore, since there is an abundence of aminopeptidases in the cells, these aminopeptidases can be used in the design of fluorogenic or fluorescent substrates for whole cell assay which otherwise will not work in cell-free enzyme assays. Therefore there is a need to develop high throughput screening (HTS) assays and reagents for such assays in whole cells which can be used for drug discovery or diagnostic procedures.
AGM-1470 (also known as TNP-470) is an angiogenesis inhibitor in clinical trials for a variety of cancers. The mechanism of action of AGM-1470 was recently discovered by two independent research groups (Sin, N., et al. Proc. Natl. Acad. Sci. U.S.A. 94:6099-6103 (1997); Griffith, E. C., et al., Chem. Biol. 4:461-471 (1997)). They found that AGM-1470 and analogs are inhibitors of methionine aminopeptidase type 2 (MetAP-2). The potency for inhibition of endothelial cell proliferation and inhibition of methionine aminopeptidase activity was determined for a series of AGM-1470 analogs and a significant correlation between the two activities was found.
Since angiogenesis inhibitors are known to be able to selectively kill cancer cells, a cellular screening assay for inhibitors of MetAP-2 may result in novel anti-cancer drugs. Therefore cell permeable fluorogenic or fluorescent substrates for MetAP-2 can be used for the screening of inhibitors of MetAP-2 in endothelial cells which could lead to novel anticancer agents.
Recently, HIV protease inhibitors such as ritonavir and viracept have been shown to be very effective in the treatment of patients infected with HIV. These inhibitors were designed based on the structure of the HIV protease substrate. The activities of these inhibitors were first determined against HIV protease. Active compounds were then tested for inhibition of HIV infection in cell cultures. A cell permeable fluorogenic or fluorescent substrate for HIV protease can be used for the screening of HIV protease inhibitors in HIV infected cells which could speed up the process for the discovery of novel HIV protease inhibitors and lead to new and better treatment for HIV infection. Since HIV protease processes viral precursor proteins at a late stage in viral replication, a cell permeable fluorogenic or fluorescent substrate for HIV protease also can be used to screen compounds which inhibit gene transcription or translation, viral entry, or other key proteins in the early stage of HIV infection. The fluorogenic or fluorescent substrates also could be used for diagnosis of HIV infection, which might be more sensitive than the currently available methods.
Applying the same principle, cell permeable fluorogenic or fluorescent substrates for cathepsin B can be used for the screening of cathepsin B inhibitors. Cell permeable fluorogenic or fluorescent substrates for dipeptidyl-peptidase IV can be used for the screening of dipeptidyl-peptidase IV inhibitors. Cell permeable fluorogenic or fluorescent substrates for renin can be used for the screening of renin inhibitors and cell permeable fluorogenic or fluorescent substrates for adenovirus protease or other viral proteases can be used for the screening of adenovirus protease or other viral protease inhibitors.
U.S. Pat. Nos. 4,557,862 and 4,640,893 disclose Rhodamine 110 derivatives as fluorogenic substrates for proteinases of the formula: 
wherein R1 and R2, which are the same or different, are selected from the group consisting of amino acids, amino acid derivatives, blocked amino acids, blocked amino acid derivatives, and peptides. Exemplary (AA)2-Rhodamines and (peptide)2-Rhodamines are (Z-Arg)2-Rhodamine 110, (Arg)2-Rhodamine 110, (Z-Ala-Arg)2-Rhodamine 110, (Z-GlN-Arg)2-Rhodamine 110, (Z-Glu-Arg)2-Rhodamine 110, (Z-Gly-Arg)2-Rhodamine 110, (Z-Leu-Arg)2-Rhodamine 110, (Z-Met-Arg)2-Rhodamine 110, (Z-Phe-Arg)2-Rhodamine 110, (Z-Pro-Arg)2-Rhodamine 110, (Z-Trp-Arg)2-Rhodamine 110, (Z-Val-Arg)2-Rhodamine 110, and (Z-Ile-Pro-Arg)2-Rhodamine 110.
WO 96/36729 discloses compounds or their salts for assaying the activity of an enzyme inside a metabolically active whole cell. The assay compound is said to include a leaving group and an indicator group. The leaving group is selected from the group comprising amino acids, peptides, saccharides, sulfates, phosphates, esters, phosphate esters, nucleotides, polynucleotides, nucleic acids, pyrimidines, purines, nucleosides, lipids and mixtures. The indicator group is selected from compounds which have a first state when joined to the leaving group, and a second state when the leaving group is cleaved from the indicator group by the enzyme. Preferred indicator compounds are said to be Rhodamine 110, rhodol, and fluorescein and analogs of these compounds. The patent application listed many enzymes and substrates of enzymes.
U.S. Pat. No. 5,576,424 disclosed haloalkyl derivatives of reporter molecules used to analyze metabolic activity in cells of the formula:
Whereinxe2x80x94BLOCK is a group selected to be removable by action of a specific analyte, to give reporter spectral properties different from those of the substrate;xe2x80x94REPORTERxe2x80x94is a molecule that, when no longer bound to BLOCK by a BLOCKxe2x80x94REPORTER bond, has spectral properties different from those of the substrate;xe2x80x94SPACERxe2x80x94is a covalent linkage; and XRxe2x80x94is a haloalkyl moiety that can covalently react with an intracellular thiol to form a thioether conjugate. Preferred reporter compounds are said to include Rhodamine-110, rhodol, fluorescein and others.
The invention relates to fluorogenic or fluorescent reporter compounds of Formula I:
x-y-zxe2x80x83xe2x80x83I
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein x and z is the same or different and is a peptide or amino acid or acyl group or other structure such that compounds of Formula I is a substrate for caspases, or a substrate for other proteases or peptidases or other enzymes; and wherein the scissile bond is only one or both of the x-y and y-z bonds in Formula I when x is the same as z, or wherein the scissile bond is only one of the x-y or y-z bond in Formula I when x is not the same as z. y is a fluorogenic or fluorescent moiety.
Preferred compounds are represented by Formula II:
R1-(AA)n-Asp-y-Asp-(AA)n-R1xe2x80x83xe2x80x83II
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein R1 is an N-terminal protecting group such as t-butyloxycarbonyl, acyl, and benzyloxycarbonyl; each AA independently is a residue of any natural or non-natural natural xcex1-amino acid or xcex2-amino acid, or derivatives of an xcex1-amino acid or xcex2-amino acid; each n is independently 0-5; and y is a fluorogenic or fluorescent moiety. Preferred y is a Rhodamine including Rhodamine 110, Rhodamine 116 and Rhodamine 19. Most preferred y is Rhodamine 110.
Especially preferred compounds are represented by Formula III: 
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein R1, AA, n are as defined previously in formula II. Preferred R1 is t-butyloxycarbonyl, acyl and benzyloxycarbonyl. Preferred values of n are 1-3.
The invention also relates to a method for the preparation of a compound of Formula III, comprising
(a) condensing Rhodamine together with N-fmoc-L-aspartic acid xcex2-t-butyl ester to give (Fmoc-Asp(OBu-t))2-Rhodamine;
(b) removing the Fmoc group to give (Asp(OBu-t))2-Rhodamine;
(c) condensing (Asp(OBu-t))2-Rhodamine with Z-(AA)n to give (Z-(AA)n-Asp(OBu-t))2-Rhodamine; and
(d) removing the OBu-t protecting group.
In a preferred embodiment, -(AA)n is WEH SEQ ID NO:1, YVA SEQ ID NO:2, LEH SEQ ID NO:3, DET SEQ ID NO:4, DEV SEQ ID NO:5, DEH SEQ ID NO:6, VEH SEQ ID NO:7, LET SEQ ID NO:8, LEV SEQ ID NO:9, SHV SEQ ID NO: 10, DEL SEQ ID NO:11, DGP SEQ ID NO:12, DEP SEQ ID NO:13, DGT SEQ ID NO:14, DLN SEQ ID NO:15, DEE SEQ ID NO:16, DSL SEQ ID NO:17, DVP SEQ ID NO:18, DEA SEQ ID NO:19, DSY SEQ ID NO:20, ELP SEQ ID NO:21, VED SEQ ID NO:22, IEP SEQ ID NO:23 or IET SEQ ID NO:24, and the carboxy containing amino acids are protected with an OBu-t group which is removed in the final step.
Another group of preferred compounds falling within the scope of Formula I include compounds wherein x is not the same as z. Preferred compounds of this group include those wherein x is a peptide or other structure which makes the compound a substrate for caspases, or a substrate for other proteases or peptidases or other enzymes; and the x-y bond in Formula I is the scissile bond under biological conditions. z is a blocking group and the y-z bond in Formula I is not a scissile bond under biological conditions.
Specifically, the novel fluorogenic or fluorescent reporter compounds of this invention are of Formula V:
R1- (AA)n-Asp-y-R6xe2x80x83xe2x80x83V
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein: R1, AA, n and y are as defined previously in formula II; and
R6 is a blocking group which is not an amino acid or a derivative of an amino acid.
In particular, preferred embodiments of the compounds of Formula V are represented by Formula VII: 
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein
R1, R6, AA and n are as defined previously in Formulae II and V;
R2 and R3 are the same or different and are independently hydrogen, alkyl or aryl; and
R4 and R5 are the same or different and are independently hydrogen or alkyl.
Another group of preferred embodiments of the compounds of Formula I are represented by Formula VIII: 
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein
R1, R6, AA and n are as defined previously in Formulae II and V; m is an integer from 0-3.
R2 and R3 are the same or different and are independently hydrogen, alkyl or aryl; and
R4 and R5 are the same or different and are independently hydrogen or alkyl.
Yet another group of preferred embodiments of the compounds of Formula I are represented by Formula IX: 
or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein
R1, R6, AA and n are as defined previously in Formulae II and V; m is an integer from 0-3.
R2 and R3 are the same or different and are independently hydrogen, alkyl or aryl; and
R4 and R5 are the same or different and are independently hydrogen or alkyl.
The invention also relates to a method for the preparation of a compound of Formula VII, comprising
(a) reacting Rhodamine with acetic anhydride to give N-acetyl-Rhodamine of Formula VI;
(b) condensing N-acetyl-Rhodamine of Formula VI together with N-fmoc-L-aspartic acid xcex2-t-butyl ester to give N-(Fmoc-Asp(OBu-t))-Nxe2x80x2-acetyl-Rhodamine;
(c) removing the Fmoc group to give N-(Asp(OBu-t))-Nxe2x80x2-acetyl-Rhodamine;
(d) condensing N-(Asp(OBu-t))-Nxe2x80x2-acetyl-Rhodamine with Z-(AA)n to give N-(Z-(AA)n-Asp(OBu-t))-Nxe2x80x2-acetyl-Rhodamine; and
(e) removing the OBu-t protecting group to give N-(Z-(AA)n-Asp)-Nxe2x80x2-acetyl-Rhodamine; or alternatively
(a) reacting Rhodamine with acetic anhydride to give N-acetyl-Rhodamine of Formula VI;
(b) condensing N-acetyl-Rhodamine of Formula VI with Z-(AA)n-Asp(xcex2-OBu-t) to give N-(Z-(AA)n-Asp(OBu-t))-Nxe2x80x2-acetyl-Rhodamine; and
(c) removing the OBu-t protecting group to give N-(Z-(AA)n-Asp)-Nxe2x80x2-acetyl-Rhodamine.
In this embodiment, where (AA)n includes amino acids such as glutamic acid or aspartic acid, the carboxy group is protected as an OBu-t group which is cleaved in the last step.
Thus, the invention also relates to the novel fluorescent dyes of Formula VI which are derivatives of Rhodamines. These compounds are prepared by introducing a blocking group R6 into one of the two amino groups of Rhodamine. The R2HN group in Formula VI provides the point of attachment for reaction with a potential enzyme substrate, such as the carboxylic group of a N-blocked peptide, to form a peptide amide bond. The reaction will convert the fluorescent molecule of Formula VI into a non-fluorescent peptide-reporter molecule of Formulae VII-IX which is a substrate for a protease or peptidase. Cleavage of the scissile peptide-reporter amide bond in peptide-reporter by proteases or peptidases produces compound of Formula VI or VIxe2x80x2 which is fluorescent.
Specifically, the novel fluorescent dyes of this invention are of Formula VI: 
or biologically acceptable salts wherein:
R2 and R3 are the same or different and are independently hydrogen, alkyl or aryl;
R6 is a blocking group which is not an amino acid or a derivative of an amino acid;
R4 and R5 are the same or different and are independently hydrogen or alkyl.
Preferred R2 and R3 are hydrogen, methyl or ethyl; Preferred R4 and R5 are hydrogen or methyl.
The invention also relates to a process of using the reporter compounds represented by Formula I to measure the activity of intracellular caspases or other enzymes involved in apoptosis in living or dead whole cells or tissues. The invention also relates to methods of using the compounds represented by Formula I and the assay processes described herein to measure the activation or inhibition of any of the caspase enzymes inside any living or dead whole cell or tissue (normal or cancerous) by a test substance or substances. The compounds represented by Formula I are cell-permeable, that is, they can be introduced into whole cells or tissue samples. The compounds are fluorogenic or fluorescent and can be designed to be specific for any of the known caspases or for any other intracellular enzymes involved in apoptosis.
Thornberry, N. A., et al., J. Biol Chem. 272:17907 (1997), describe the optimal sequences for various caspase substrates and for the Granzyme B substrate. The optimal substrate sequences are shown in Table 1.
Using the optimal sequences described by Thornberry et al., fluorogenic or fluorescent substrates for specific caspases can be synthesized by the procedures described herein.
It is also possible to design other fluorogenic or fluorescent substrates for known or unknown caspases by utilizing known or potential cleavage site peptide sequences from known or potential natural substrates of caspase enzymes. Table 2 depicts peptide sequences corresponding to known or potential cleavage sites in proteins that may be natural substrates for caspases.
The fluorogenic or fluorescent substrates can also be designed to measure more than one enzyme at a time, by designing substrates that are recognized and cleaved by more than one of the enzymes involved in the caspase cascade. Fluorogenic or fluorescent substrates which are xe2x80x9cpromiscuousxe2x80x9d for more than one caspase may be utilized using the assay process described herein to measure the activity of as yet unknown caspases.
When the caspase cascade is activated by a cell-death inducing stimulus, the fluorogenic or fluorescent reporter molecules described herein are cleaved and respond with a large increase in fluorescence emission. The change in fluorescence can be measured spectrofluorometrically. The reporter molecules can also be used to measure baseline caspase activity in cells that are not undergoing apoptosis. The method is easily adaptable to high throughput or ultra-high throughput screening assays.
The assay system is very versatile. Examples of the extreme versatility of the assay system are given below:
1. The assay can be used to screen a cell or tissue for baseline activity of any caspase enzyme or any other enzyme involved in apoptosis.
2. The assay can be used with equal ease to screen for compounds that can either activate or inhibit the caspase cascade. That means the assay can be used to screen for drugs against degenerative diseases or for drugs against cancer.
3. The assay can be used to screen for caspase cascade activation or inhibition in any living or dead cells or cell lines derived from any organ system in the body including, but not limited to, hair, brain, peripheral nervous system, eye, ear, nose, mouth, tonsils, teeth, esophagus, lung, heart, blood, blood vessels, bone marrow, lymph nodes, thymus, spleen, immune system, liver, stomach, intestinal tract, pancreas, endocrine glands and tissues, kidney, bladder, reproductive organs and glands, joints, bones and skin. The assay can be used to screen for drugs with potential use in any disease of any organ system in the body that involves malfinction of the caspase cascade.
4. The assay can be used to screen for drugs that might modulate the caspase cascade directly or indirectly, i.e. by modulating the caspases itself or by modulating cellular receptors and co-factors that influence the caspase cascade.
5. The assay can be used to determine the site of action at which a caspase cascade modulator interferes. That is, the assay can help to pin down the molecular mechanism of action of a novel caspase cascade modulator drug.
The invention also relates to the use of the fluorogenic or fluorescent substrates represented by Formula I for finding new compounds or new uses for known compounds in reducing, preventing or treating maladies in which apoptotic cell death is either a causative factor or a result. Examples of uses for the present invention include screening for compounds that can protect the nervous system following focal ischemia and global ischemia; screening for compounds that can treat neurodegenerative disorders such as Alzheimer""s disease, Huntington""s Disease, prion diseases, Parkinson""s Disease, multiple sclerosis, amyotrophic lateral sclerosis, ataxia, telangiectasia, and spinobulbar atrophy; screening for compounds that can treat heart disease including myocardial infarction, congestive heart failure and cardiomyopathy; screening for compounds that can treat retinal disorders; screening for compounds that treat autoimmune disorders including lupus erythematosus, rheumatoid arthritis, type I diabetes, Sjxc3x6gren""s syndrome and glomerulonephritis; screening for compounds that treat polycystic kidney disease and anemia/erythropoiesis; screening for compounds that treat immune system disorders, including AIDS and SCIDS; screening for compounds that reduce or prevent cell, tissue and organ damage during transplantation (e.g. graft versus host disease in bone marrow transplantation procedures); screening for compounds that reduce or prevent cell line death in industrial biotechnology; screening for compounds that reduce or prevent alopecia (hair loss); and screening for compounds that reduce the premature death of skin cells.
The present invention also relates to the use of the fluorogenic or fluorescent substrates represented by Formula I in screening procedures where libraries of known drugs or combinatorial or other compound libraries are screened for compounds with anti-tumor or anti-cancer activity. The cancer cells or cell lines can be derived from any cancer of any internal or external organ system in the body including, but not limited to brain, peripheral nervous system, eye, ear, nose, mouth, tonsils, teeth, esophagus, lung, heart, blood, blood vessels, bone marrow, lymph nodes, thymus, spleen, immune system, liver, stomach, intestinal tract, pancreas, endocrine glands and tissues, kidney, bladder, reproductive organs and glands (e.g. prostate gland), joints, bones and skin.
The present invention also relates to the use of the fluorogenic or fluorescent substrates represented by Formula I in diagnostic procedures to determine the chemosensitivity or resistance of cancer cells taken from an animal or a human being to treatment with chemotherapeutic drugs. The cancer cells or cell lines can be derived from any cancer of any internal or external organ system in the body including, but not limited to brain, peripheral nervous system, eye, ear, nose, mouth, tonsils, teeth, esophagus, lung, heart, blood, blood vessels, bone marrow, lymph nodes, thymus, spleen, immune system, liver, stomach, intestinal tract, pancreas, endocrine glands and tissues, kidney, bladder, reproductive organs and glands (e.g. prostate gland), joints, bones and skin.
In particular, the invention relates to a method for detecting an enzyme involved in the apoptosis cascade in one or more cells, comprising
(a) contacting the one or more cells with a reporter compound according to the invention under conditions whereby the reporter compound is taken into said one or more cells, and
(b) recording the fluorescence of said one or more cells, wherein a change in fluorescence, either of magnitude (i.e. increase) or of wave length, within the one or more cells compared to control cells which have not been so contacted or one that has been contacted with the reporter compound and a known competitive inhibitor of the enzyme, is an indication of the presence of the enzyme.
The invention also relates to a method for measuring the activity of an enzyme involved in the apoptosis cascade in one or more cells, comprising
(a) contacting the one or more cells with the reporter compound according to the invention under conditions whereby said reporter compound is taken into the one or more cells, and
(b) recording the fluorescence of the one or more cells, wherein the relative change in fluorescence, either of magnitude or of wave length within the one or more cells, compared to control cells which have not been so contacted or one that has been contacted with the reporter compound and a known competitive inhibitor of the enzyme, is a measure of the activity of the enzyme.
The invention also relates to a method for determining whether a test substance has an effect on an enzyme involved in the apoptosis cascade in one or more test cells, comprising
(a) contacting the one or more test cells with the test substance and the reporter compound according to the invention under conditions whereby the reporter compound is taken into the one or more cells and the test substance either interacts with an external membrane receptor or is taken into said cells, and
(b) recording the fluorescence of the test cells, wherein a change in fluorescence, either of magnitude or of wavelength, within the cells compared to the control cells which have only been contacted with the reporter compound and not with the test substance, is an indication that the test substance has an effect either directly or indirectly on the apoptosis enzyme being tested.
In the practice of this aspect of the invention, the test cells may be contacted with said test substance prior to, after, or substantially simultaneously with the reporter compound according to the invention. The method may be used to detect whether the test substance stimulates or inhibits the activity of the enzyme.
The invention also relates to further contacting the test cells with a second test substance or mixture of test substances in the presence of the first test substance.
In a preferred embodiment, the test cell is a cancer cell or cell line derived from a human in need of treatment with a chemotherapeutic drug and the test substance is a chemotherapeutic agent or a mixture of chemotherapeutic agents.
The invention also relates to a method to determine the sensitivity of an animal with cancer to treatment with one or more chemotherapeutic agents, comprising
(a) contacting cancer cells taken from said animal with one or more chemotherapeutic agents and the reporter compound according to the invention under conditions whereby the reporter compound is taken into the cancer cells and the one or more drugs either interact with an external membrane receptor or are taken into the said cell, and
(b) recording the fluorescence of the cancer cells, wherein a change in fluorescence, either of magnitude or of wavelength, within the cancer cells compared to control cells which have only been contacted with the reporter compound, is an indication that the cancer cells are chemosensitive to the one or more agents and that the animal is sensitive to the treatment.
The invention also relates to a method to monitor the treatment of an animal with one or more chemotherapeutic drugs, comprising
(a) administering one or more chemotherapeutic drugs to the animal,
(b) contacting cells taken from the animal after administering the reporter compound according to the invention under conditions whereby the reporter compound is taken into the cells, and
(c) recording the fluorescence of the cells contacted with the reporter compound, wherein a change in fluorescence, either of magnitude or of wavelength, within the cells taken from the animal after administering compared to the control cells which have been taken from the animal before the administration is an indication that the animal is sensitive to the chemotherapeutic agent. In this embodiment, the animal may suffer from a malady in which apoptotic cell death is either a causative factor or a result.
The invention also relates to a method for determining whether a test substance inhibits or prevents cell death in one or more test cells, comprising
(a) contacting the test cell with the test substance and the reporter compound according to the invention under conditions whereby the test substance either interacts with an external membrane receptor or is taken into the cell and the reporter compound is taken into the cell, and
(b) recording the fluorescence of the test cells, wherein a change in fluorescence, either of magnitude or of wavelength, within the test cells compared to control cells that have only been contacted with the reporter compound, is an indication that the test substance inhibits or prevents cell death.
The invention also relates to a method for determining whether a test substance causes or enhances cell death in one or more test cells, comprising
(a) contacting the test cells with the test substance and the reporter compound according to the invention under conditions whereby the test substance either interacts with an external membrane receptor or is taken into the cells and the reporter compound is taken into the cells,
(b) recording the fluorescence of the test cells, wherein a change in fluorescence, either of magnitude or of wavelength, within the test cells compared to control cells which have only been contacted with the reporter compound, is an indication that the test substance causes or enhances cell death.
The invention also relates to a process of using the reporter compounds represented by Formula IX to measure the activity of intracellular peptidases and proteases in living whole cells, including, but not limited to, type-2 methionine aminopeptidase in endothelial cells and HIV protease in HIV infected cells. The invention also relates to methods of using the compounds represented by Formula IX and the assay processes described herein to measure the inhibition or activation of enzymes inside living whole cell by a test compound or compounds. The reporter compounds represented by Formula IX are cell-permeable, that is they can be introduced into whole cells. The compounds are fluorogenic or fluorescent and can be designed to be specific for the known enzymes of interest, such as methionine aminopeptidase or HIV protease.
The invention also relates to a method for detecting a viral protease in one or more cells, comprising
(a) contacting the cells with the reporter compound according to the invention under conditions whereby the reporter compound is taken into the cells, and
(b) recording the fluorescence of said cells, wherein a change or increase in fluorescence within the cells compared to control cells which have not been so contacted is an indication of the presence of the viral protease.
The invention also relates to a method for measuring the activity of a viral protease in one or more viral infected cells, comprising
(a) contacting the one or more viral infected cells with the reporter compound according to the invention under conditions whereby the reporter compound is taken into the one or more viral infected cells, and
(b) recording the fluorescence of said one or more cells, wherein a change or increase in fluorescence within the one or more viral infected cells compared to control cells which have not been so contacted is a measure of the activity of the viral protease.
The invention also relates to a method for determining whether a test substance has an effect on the activity of viral protease in one or more viral infected cells, comprising
(a) contacting the viral infected test cells with the test substance and the reporter compound according to the invention under conditions whereby said reporter compound is taken into the infected test cells, and
(b) recording the fluorescence of the infected test cells compared to infected control cells which have only been contacted with the reporter compound, wherein a change or increase in fluorescence within the infected test cells compared to the infected control cells is an indication that the test substance has an effect, on the viral protease.
In a preferred embodiment, the cells are HIV infected cells and the viral protease is HIV protease. In another preferred embodiment, the cells are adenovirus infected cells and the viral protease is adenovirus protease. In another preferred embodiment, the cells are HSV infected cells and the viral protease is HSV protease. In another preferred embodiment, the cells are HCMV infected cells and the viral protease is HCMV protease. In another preferred embodiment, the cells are HCV infected cells and the viral protease is HCV protease.
The invention also relates to a method for measuring the activity of protease or peptidase in cells, comprising
(a) contacting the test cells with the reporter compound according to the invention under conditions whereby the reporter compound is taken into the test cells, or the reporter compound is interacting with an external membrane protease or peptidase of said cells, and
(b) recording the fluorescence of the cells, wherein a change or increase in fluorescence within the test cell compared to control cells which have not been so contacted is a measure of the activity of the the protease or peptidase.
The invention also relates to a method for determining whether a test substance has an effect on the activity of protease or peptidase in the test cells, comprising
(a) contacting the test cells with the test substance and the reporter compound according to the invention under conditions whereby the reporter compound is taken into the test cells, or the reporter compound is interacting with an external membrane protease or peptidase of the cells, and
(b) recording the fluorescence of the test cells compared to control cells which have only been contacted with the reporter compound, wherein a change or increase in fluorescence within the test cells compared to the control cells is an indication that the test substance has an effect on the protease or peptidase.
In a preferred embodiment, the cells are endothelial cells and the peptidase is type 2 methionine aminopeptidase. In anther preferred embodiment, cells are T cells and the peptidase is dipeptidyl peptidase-IV. In another preferred embodiment, the cells are neuron cells and the protease is calpain.